With increasing cost of fossil fuel energy, alternate emergy sources have become economically feasible. Among these sources is wind power. Wind power has always suffered from its unpredictability from day to day and season to season. The creation over the last few decades of the national electric power grid and large centralized fossil fuel-powered generators, however, has to some extent alleviated this problem. Conventional fossil (and nuclear) electric generation can provide power in individual locations when wind velocity is not high enough to permit self-sustaining operation. The electric power grid provides a means for transmitting an excess of wind power in a local area to users in remote areas.
Among the types of wind turbines employed as prime movers in wind generation systems is the so-called Darrieus or "egg beater" turbine. These turbines are formed of thin flexible ribbons attached at their ends to a central rotating shaft and have an aerodynamic cross-section. Wind blowing across the ribbons generates lift on them. Centripetal force maintains the ribbons in a taut catenary curve when the shaft is rotating, so the tangential stiffness thereby created transforms the lift into torque on the shaft. The advantages of the Darrieus turbine are the extreme simplicity and low cost, omnidirectionality respecting wind, and the vertical axis of rotation precluding the necessity for a gear box or a generator mounted aloft adjacent to the turbine. The great disadvantage inherent with Darrieus turbines is the fact that they have no starting torque. When not rotating, the wind blowing across the ribbons cannot act on their profiles to create lift on them.
In copending application Ser. No. 06/389523, having a common filing data with this application, Gale Jallen as applicant, and entitled "Wind Driven Induction Generator," an induction generator driven by a wind turbine and connected to it by an overriding clutch is disclosed. The use of the overriding clutch prevents the generator from using electric power from the grid as a motor to turn the turbine when wind speed is not itself sufficient to rotate the turbine at a speed causing negative slip and thus inducing electric generation by the generator.
A wind electric system employing a Darrieus turbine forms the subject of U.S. Pat. No. 4,112,311. Aviation Week and Space Technology, July 14, 1980, at page 81 and especially at page 89 discusses the Darrieus turbine. U.S. Pat. No. 3,596,105 teaches the use of a motor/generator for a starter for jet engines, and after starting for a generator for engine and airplane accessories.